1. Field of the Invention
The present invention relates to an improvement of continuous mixer and operating method thereof, and more precisely, a continuous mixer and operating method thereof to enable a main motor to easily re-operate the continuous mixer after an emergency stop by discharging a raw material to be mixed in a barrel prior to the re-operation.
2. Description of the Related Art
One constitution is known as will hereinafter be described for example as a continuous mixer for mixing a raw material such as powdery, pellet-like or granular resin etc. which is fed into a feed zone from a feeder through a hopper and a feed port. The present invention will be more fully understood from the following description of a twin continuous mixer as an example of continuous mixer when reference is made to FIG. 6, a side cross-sectional view showing the overall structure of the twin continuous mixer.
The numeral 51 shown in FIG. 6 indicates a twin continuous mixer, which comprises a barrel 52, wherein an approximately cylindrical twin chamber 53 in the longitudinal direction is formed to be communicated through an approximately spectacle-shaped cross-section. In the chamber 53, a pair of left and right rotors 54 (hereinafter referred to as screw) for feeding a raw material to be mixed from one end side (upstream side, that is, right-hand side of FIG. 6) of the barrel 52 to the other end side (downstream side, that is, left-hand side of FIG. 6), and for mixing and melting in the mid-flow thereof, are penetrated in parallel to each other freely rotatably. Bearings 55, 56 and 57 are provided on the upstream and downstream side of the barrel 52. Each of the screws 54, the end parts in the axial direction of which being supported freely rotatably by the bearings 55, 56 and 57, is constituted to be rotatably driven in different directions with each other so that the inner side opposing to the pair moves from above to below.
A driving unit 58 is connected at the upstream side end of the barrel 52 for the screws 54. The driving unit 58 comprises a casing 59 connected tandemly to the upstream side end of the barrel 52, a pair of front and rear bearings 55 and 56 for supporting freely rotatably a driving axis member 60 of the par of screws 54, 54 penetrated in the casing 59, and a driving gear 61 fixed in the longitudinal middle of the driving axis member 60. The driving axis member 60 of one of the screws 54, 54 protrudes outward to the further upstream side of the casing 59. The end of the protruding driving axis member is connected to a motor 62 with reduction gear. The driving gears 61 for each screw 54, 54, which are engaged each other, are constituted so that in the case one of the screws 54 is rotatably driven by the motor 62, the other is rotated in another direction.
On the upper surface side of the upstream side end of the barrel 52 is provided a feed port 63, for feeding raw material to be mixed into the mixing chamber 53. A hopper not shown is connected to the feed port 63. In the intermediate part of the barrel 52 is formed a vent hole 64 for degassing the gas both entrained when feeding raw material and generated during mixing, from the chamber 53. On the lower surface side of the downstream side end of the barrel 52 is also provided a discharge port 65 downward for discharging melted mixed material outside the barrel 52. Further, in the middle of the raw material conveying direction of the barrel 52 is provided a gate device 67 for adjusting the flow rate of the raw material by bringing/pulling a pair of above and below gate plates 66 close to/away from the outer circumference of the screw 54 outward radially. Therefore the chamber 53 in the barrel 52 is partitioned into two mixing zone 53a and 53b, each of which being arranged tandemly respectively on the upstream and downstream side of the gate device 67.
On the outer circumference of the screw 54 penetrated in the first mixing zone 53a of the two mixing zone above, which is arranged on the upstream side of the gate device 67, is formed in order from the upstream side a first feed part 68 for feeding forward the raw material to be mixed fed through the feed port 63, and a first mixing part 69 for mixing and melting the raw material by adding a strong shearing force thereto. Meanwhile, on the outer circumference of the screw 54 penetrated in the second mixing zone 53b, which is arranged on the downstream side of the gate device 67, is formed a second feed part 70 for conveying the mixed material melted in the first mixing part 69 forcibly toward the discharge port 65 (refer to Japanese Patent Laid-Open Publication No. 2001-9830 for example).
In accordance with a continuous mixer related to the above-described prior art, a raw material to be mixed comprising either powdery, pellet-like or granular resin, which is fed from the feeder, is fed into the first feed part through the feed port. The raw material to be mixed, which is fed into the first feed part, is conveyed to the first mixing part in the first mixing zone on by a screw being normally rotated, wherein to be mixed and melted, and also to a second mixing zone on the downstream side of the gate device. The material being mixed and melted, which is fed into the second mixing zone, is forcibly conveyed toward the discharge port by the second feed part of the screw, and then discharged outside the mixer through the discharge port.
The screw of the continuous mixer is constituted to be rotatably driven by a main motor with reduction gear as described above. The main motor starts with a low starting torque after discharging a residual material in the barrel through the discharge port before starting the operation of the continuous mixer. Therefore, there is provided a burring motor of small capacity other than the main motor for rotating the screw at low speed to discharge the residual material before starting the operation.
In the case of the continuous mixer being emergently stopped due to some kind of reason, there may arise a situation, depending on the stop timing of the feeder on the upstream side, that large amounts of residual materials containing a raw material to be mixed and/or a mixed material stay in the chamber in the barrel.
In spite of the effort to discharge such large amounts of residual materials in the chamber by rotating the screw using the burring motor, since another residual material consisting of raw material to be mixed before melting, which is left in the first feed part, may be pressed, it is impossible to discharge a residual material in the chamber completely through the discharge port, resulting in that the restarting of the continuous mixer may become difficult.
To start the operation of the continuous mixer by starting the main motor with a low starting torque is based on the following reason. That is, a motor that can provide a 100% torque from the rising is expensive and also the frame number becomes higher due to the design thereof own. In general, main motor of as much as several thousand KW is usually designed with the starting torque being restricted, wherein a current limit may be made when starting depending on the power facility of the plant. For instance, in the case of a main motor which provides a 40% starting torque, a burring motor (of an approximately 60% capacity) is used to check before driving if the main motor can be driven with a torque of 40% or less.